U.S. patent application number 10/683110 was filed with the patent office on 2005-04-14 for linear control device for controlling a resistive and/or an inductive and/or a capacitive load.
This patent application is currently assigned to ASTRAL COMMUNICATIONS, INC.. Invention is credited to Hall, Mark E., Kazanov, Anatoly L., Paige, Anthony.
Application Number | 20050077840 10/683110 |
Document ID | / |
Family ID | 34422663 |
Filed Date | 2005-04-14 |
United States Patent
Application |
20050077840 |
Kind Code |
A1 |
Kazanov, Anatoly L. ; et
al. |
April 14, 2005 |
LINEAR CONTROL DEVICE FOR CONTROLLING A RESISTIVE AND/OR AN
INDUCTIVE AND/OR A CAPACITIVE LOAD
Abstract
An energy savings device for an inductive, resistive or
capacitive load that is powered by an input AC voltage waveform,
whereby the load may be a fluorescent lighting fixture. A setting
unit allows a user to set a desired power operating level for the
load, and outputs a setting signal as a result thereof. A processor
receives the setting signal from the setting unit, and determines a
phase delay to be performed on an output AC voltage waveform that
is to be provided to the load, wherein the processor outputs a
control signal as a result thereof. A switching linear control
element receives the control signal output from the processor, and
turns off and on at predetermined times in accordance with the
control signal, so as to create the output AC voltage waveform as a
chopped voltage waveform from the input AC voltage waveform. A
bridge rectifier is connected to the switching linear control
element and disposed in a series connection between the load and a
line that provides the input AC voltage waveform, which converts an
AC current waveform from a bi-directional waveform to a
uni-directional waveform for inputting to the switching linear
control element.
Inventors: |
Kazanov, Anatoly L.;
(Reisterstown, MD) ; Hall, Mark E.; (Bowie,
MD) ; Paige, Anthony; (Fort Washington, MD) |
Correspondence
Address: |
FOLEY AND LARDNER
SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
ASTRAL COMMUNICATIONS, INC.
|
Family ID: |
34422663 |
Appl. No.: |
10/683110 |
Filed: |
October 14, 2003 |
Current U.S.
Class: |
315/294 ;
315/207; 315/291; 315/86 |
Current CPC
Class: |
H05B 39/048 20130101;
H05B 41/3924 20130101 |
Class at
Publication: |
315/294 ;
315/086; 315/291; 315/207 |
International
Class: |
H05B 041/36 |
Claims
What is claimed is:
1. An energy savings device for an inductive, resistive or
capacitive load that is powered by an input AC voltage waveform,
comprising: a setting unit configured to allow a user to set a
desired power operating level for the load, and that outputs a
setting signal as a result thereof; a processor configured to
receive the setting signal from the setting unit, and that
determines a phase delay to be performed on an output AC voltage
waveform that is to be provided to the load, wherein the processor
outputs a control signal as a result thereof; a switching linear
control element that receives the control signal output from the
processor, and that turns off and on at predetermined times in
accordance with the control signal, so as to create the output AC
voltage waveform as a chopped voltage wavefrom from the input AC
voltage waveform; and a bridge rectifier connected to the switching
linear control element and disposed in a series connection between
the load and a line that provides the input AC voltage waveform,
wherein the bridge rectifier converts an AC current waveform from a
bi-directional waveform to a unidirectional waveform for inputting
to the switching linear control element, wherein the output voltage
waveform is provided to the load by way of the bridge
rectifier.
2. The energy savings device according to claim 1, wherein the
switching linear control element comprises a metal oxide
semiconductor field effect transistor (MOSFET).
3. The energy savings device according to claim 1, wherein the
switching linear control element comprises a bi-junction transistor
(BJT).
4. The energy savings device according to claim 1, wherein the
switching linear control element comprises an insulated gate
bipolar transistor (IGBT).
5. The energy savings device according to claim 1, wherein the load
is a fluorescent light fixture having either a magnetic ballast or
an electronic ballast.
6. The energy savings device according to claim 5, further
comprising: a motion detector configured to detect any motion
within a particular area, and to provide a motion signal to the
processor indicative as to whether or not any motion is detected,
wherein the processor is configured to control a dimming level of
the fluorescent light fixture based in part on the motion
signal.
7. An energy savings method for an inductive, resistive, or
capacitive load that is powered by an input AC voltage waveform,
the method comprising: setting a desired power operating level for
the load; receiving, by a processor, a signal indicative of the
desired power operating level for the load, and determining a phase
delay to be performed on an output AC voltage waveform that is to
be provided to the load, and to output a control signal as a result
thereof; in response to the control signal, turning a switching
linear control element off and on at predetermined times in
accordance with the control signal, so as to create the output AC
voltage waveform from the input AC voltage waveform; and
converting, by way of a bridge rectifier connected to the switching
linear control element and disposed in a series connection between
the load and a line that provides the input AC voltage waveform, an
AC current waveform received on the line from a bi-directional
waveform to a unidirectional waveform for inputting to the
switching linear control element.
8. The energy savings method according to claim 7, wherein the
switching linear control element comprises a metal oxide
semiconductor field effect transistor (MOSFET).
9. The energy savings method according to claim 7, wherein the
switching linear control element comprises a bi-junction transistor
(BJT).
10. The energy savings method according to claim 7, wherein the
switching linear control element comprises an insulated gate
bipolar transistor (IGBT).
11. The energy savings method according to claim 7, wherein the
load is a fluorescent light fixture having either a magnetic
ballast or an electronic ballast.
12. The energy savings method according to claim 11, further
comprising: detecting any motion within a particular area, and
providing a motion signal to the processor indicative as to whether
or not any motion is detected; and controlling a dimming level of
the fluorescent light fixture by the processor based in part on the
motion signal.
13. A computer program product being executed by a processor and
which provides an energy savings capability for an inductive,
resistive or capacitive load that is powered by an input AC voltage
waveform, the computer program product comprising: first program
product code for setting a desired power operating level for the
load; second program product code for determining a phase delay to
be performed on an output AC voltage waveform that is to be
provided to the load, and to output a control signal as a result
thereof; third program product code for a switching linear control
element off and on at predetermined times in accordance with the
control signal, so as to create the output AC voltage waveform from
the input AC voltage waveform; and fourth program product code for
converting an AC current waveform on the line from a bi-directional
waveform to a unidirectional waveform for inputting to the
switching linear control element, wherein a bridge rectifier that
is disposed in series between the line and the load provides the
output AC voltage waveform to the load.
14. The computer program product according to claim 13, wherein the
switching linear control element comprises a metal oxide
semiconductor field effect transistor (MOSFET).
15. The computer program product according to claim 13, wherein the
switching linear control element comprises a bi-junction transistor
(BJT).
16. The computer program product according to claim 13, wherein the
switching linear control element comprises an insulated gate
bipolar transistor (IGBT).
17. The computer program product according to claim 13, wherein the
load is a fluorescent light fixture having either a magnetic
ballast or an electronic ballast.
18. The computer program product according to claim 13, further
comprising: fifth program product code for detecting any motion
within a particular area, and providing a motion signal to the
processor indicative as to whether or not any motion is detected;
and sixth program product code for controlling a dimming level of
the fluorescent light fixture by the processor based in part on the
motion signal.
Description
BACKGROUND OF THE INVENTION
[0001] A. Field of the Invention
[0002] The invention relates to an energy savings device or method
that can be applied to a resistive, an inductive, or a capacitive
load regardless of the respective impedance or inductance or
capacitance of the load. More particularly, the invention relates
to a linear control dimming device that is mounted in series with a
resistive, an inductive or a capacitive load and that has access
for power and operation to one side of an electrical line supplied
to the load. A fluorescent light fixture or a motor for a fan or
other device, for example, can be controlled by way of the linear
control device or method according to the invention.
[0003] B. Description of the Related Art
[0004] The ability to control illumination levels is strongly
desired, especially due to the rising energy costs. Such ability to
control illumination levels is very important for establishments
that require a great deal of lighting, such as restaurants and
offices.
[0005] Lighting levels that are higher than necessary not only
result in a higher energy costs associated with the lighting, but
also can increase air conditioning costs due to the excess heat
provided by the lighting fixtures. Fluorescent light fixtures
output less heat than incandescent light fixtures for equivalent
illumination, and thus they are becoming more popular with offices
or other commercial establishments.
[0006] There currently exist various types of dimmer devices that
can be used in order to control the amount of light output by
fluorescent lights. One type utilizes a complex electronic ballast
which first converts the applied AC line voltage to DC, then
switches the applied tube voltage at high frequency. The resulting
power-to-light output efficiency is hampered by this additional
manipulation. This type requires an expensive fixture replacement
and rewiring to the wall switch. Simplistic phase control devices
will not provide satisfactory results when controlling a magnetic
ballast fluorescent fixture.
[0007] FIG. 1A shows the connections of a conventional fluorescent
dimmer device or controller 100, which is provided between a line
and a load. The load is shown as a light fixture 110, which may be
a fluorescent tube and associated ballast, for example. As shown in
FIG. 1A, the conventional controller 100 needs access to both sides
(line 102 and neutral 104) of an AC power input, in addition to the
load. Since connectivity to the neutral line 104 is not always
available at a light switch box, conventional fluorescent
controllers may require expensive re-wiring to be installed.
[0008] The problem with using such a conventional dimmer circuit
for a fluorescent lighting fixture is that the conventional dimmer
circuit cannot modulate reactive loads. Reactive loads react with
the controller, thereby producing oscillations that then cause
surges of voltage and current, which are both unpredictable and
uncontrollable. With such control being applied to a fluorescent
light fixture, the typical result is a non-harmonic type of
flickering, which frequently takes the light from zero output to
maximum output and to values in between. Such flickering is
visually (and also audibly) discomforting, and may even be
unhealthful to people who are near the flickering fluorescent light
(for example, it may cause headaches due to having to view the
undesirable light flickering).
[0009] As explained earlier, a controller such as the one shown in
FIG. 1A can be used to control a fluorescent light without causing
significant flickering, but such a controller requires fairly
substantial installation costs, since they cannot be installed at a
light switch box (where a neutral line is not typically provided),
but rather have to be installed very close to the ballast (e.g., in
the ceiling of a room, where a neutral line is provided).
[0010] U.S. Pat. No. 5,043,635 to Talbott et al. describes a two
line power control device for dimming fluorescent lights, which
does not require to be coupled to a neutral line. Accordingly, the
Talbott et al. device can in theory be installed at a light switch
box. However, due to the analog structure and the various
components described in the Talbott et al. device, such a device is
very difficult to manufacture, and also such a device is very
difficult to manufacture in a small size. Thus, it is not feasible
to install such a device in a light switch box, given the bulkiness
as well as the transformer configuration of the Talbott et al.
device.
SUMMARY OF THE INVENTION
[0011] The present invention is directed to an apparatus and a
method for controlling an amount of power supplied to a resistive,
inductive or capacitive load by modulating a period of time that
current flows through the load.
[0012] According to one aspect of the invention, there is provided
an energy savings device for an inductive, resistive or capacitive
load that is powered by an input AC voltage waveform. The device
includes a setting unit configured to allow a user to set a desired
power operating level for the load, and that outputs a setting
signal as a result thereof. The device also includes a processor
configured to receive the setting signal from the setting unit, and
that determines a phase delay to be performed on an output AC
voltage waveform that is to be provided to the load, wherein the
processor outputs a control signal as a result thereof. The device
further includes a switching linear control element that receives
the control signal output from the processor, and that turns off
and on at predetermined times in accordance with the control
signal, so as to create the output AC voltage waveform as a chopped
voltage wavefrom from the input AC voltage waveform. The device
still further includes a bridge rectifier connected to the
switching linear control element and disposed in a series
connection between the load and a line that provides the input AC
voltage waveform, wherein the bridge rectifier converts an AC
current waveform from a bi-directional waveform to a unidirectional
waveform for inputting to the switching linear control element. The
output voltage waveform is provided to the load by way of the
bridge rectifier.
[0013] According to another aspect of the invention, there is
provided an energy savings method for an inductive, resistive, or
capacitive load that is powered by an input AC voltage waveform.
The method includes setting a desired power operating level for the
load. The method also includes receiving, by a processor, a signal
indicative of the desired power operating level for the load, and
determining a phase delay to be performed on an output AC voltage
waveform that is to be provided to the load, and to output a
control signal as a result thereof. The method further includes, in
response to the control signal, turning a switching linear control
element off and on at predetermined times in accordance with the
control signal, so as to create the output AC voltage waveform from
the input AC voltage waveform. The method still further includes
converting, by way of a bridge rectifier connected to the switching
linear control element and disposed in a series connection between
the load and a line that provides the input AC voltage waveform, an
AC current waveform received on the line from a bi-directional
waveform to a unidirectional waveform for inputting to the
switching linear control element.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The foregoing advantages and features of the invention will
become apparent upon reference to the following detailed
description and the accompanying drawings, of which:
[0015] FIG. 1A shows a hookup of a related energy savings device
that is provided between an input voltage line and a load;
[0016] FIG. 1B shows a hookup of a related energy savings device
that is provided between an input voltage line and a load;
[0017] FIG. 2 shows an alternative hookup of a related energy
savings device that provides neutral side control;
[0018] FIG. 3 is a block diagram of a first related energy savings
device;
[0019] FIG. 4 is a schematic circuit diagram of the first related
energy savings device;
[0020] FIG. 5 shows phase control waveforms according to the first
related energy savings device;
[0021] FIG. 6 is a software flow diagram of microprocessor firmware
that operates the first related energy savings device;
[0022] FIG. 7 is a block diagram of a second related energy savings
device;
[0023] FIG. 8 is a schematic circuit diagram of the second related
energy savings device;
[0024] FIG. 9 is a schematic circuit diagram of a master unit used
in a related energy savings device;
[0025] FIG. 10 is a schematic circuit diagram of a follower unit
used in a related energy savings device;
[0026] FIG. 11 is a block diagram of an energy savings device
according to a first embodiment of the invention;
[0027] FIGS. 12A, 12B and 12C show phase control waveforms
according to the first embodiment of the invention; and
[0028] FIG. 13 is a schematic circuit diagram of an energy savings
device according to the first embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0029] Preferred embodiments of the invention will be described in
detail below, with reference to the accompanying drawings.
[0030] The invention is directed to an apparatus and method for
controlling power to a resistive, an inductive or a capacitive
load, such as a fluorescent light fixture, a halogen light fixture,
or a motor for a fan. In a preferred configuration, the energy
controlling apparatus is configured to be installed in a light
switch box typically located on an interior wall of a building,
behind a wall switch plate. Since most light switches are mounted
within a switch box that is easily accessible through the wall
(e.g., behind a switch plate), the line to the switch is dropped
from the fixture to the switch, and the other side of the line
(e.g., neutral) is not conveniently present. The invention provides
a true switch replacement and operates in series with an inductive
or resistive load, in a two-wire configuration, plus safety ground
wire.
[0031] Before describing the invention, also referred to below as a
linear control device or LCD, a related device referred to as a
universal control device or UCD, which is described in U.S. patent
application Ser. Nos. 10/454,840, filed Jun. 5, 2003, and Ser. No.
10/205,031, filed Jul. 26, 2002, which are assigned to the same
entity as this application and which are incorporated in their
entirety herein by reference, will be explained below.
[0032] FIG. 1B shows a hookup of a Universal Control Device (UCD)
energy savings device 150, which is provided between the input AC
line voltage 102 and a reactive load 110, whereby hookup to the
neutral line 104 is not required by the energy savings device 150
in order to provide an energy control function for the load
110.
[0033] Additionally, referring now to FIG. 2, some installations
will wire the line 102 directly to the light fixture 110, leaving
the load return 103 for fixture control. In this case, there is no
line 102 connection in the switch box, again disallowing
integration of a conventional fluorescent dimmer device. The UCD
controller 150 is fully compatible with neutral 104 side control,
in the manner as shown in FIG. 2. In summary, the UCD controller is
installed in series with the load, on either side of the load,
without regard to wiring polarity, identically to a dry contact
switch installation.
[0034] With regards to fluorescent light fixtures, the UCD energy
savings device regulates a voltage output to gaseous discharge
lamps of the fluorescent light fixture from the secondary coils of
a ballast element of the fluorescent light fixture.
[0035] A block diagram of the UCD is shown in FIG. 3, and a
schematic circuit diagram of the UCD is shown in FIG. 4.
[0036] The UCD includes a "push" On/Off switch and potentiometer
unit 310 that is coupled to a line input (AC input voltage) 305, a
solid state switch unit 320, a driver 330 for driving the solid
state switch unit 320, a power supply 340, a microprocessor 350,
and a line synchronization detector 360. The solid state switch
unit 320 is provided between the line input 305 and the load 365.
The switch and potentiometer unit 310 includes a "push" On/Off
switch SW1 and a potentiometer POT. The line synchronization
detector 360 provides an interrupt signal to the microprocessor
350, which corresponds to "rising" zero crossing of a load current
waveform, to be explained in more detail below.
[0037] The UCD is a two wire dimmer unit, and can be utilized to
control standard magnetic fluorescent fixtures. The UCD may also be
used to control other resistive, inductive or capacitive (e.g.,
standard electronic fluorescent fixtures) loads. The UCD functions
similar to incandescent dimmers, but it also implements line
synchronization functions and timing functions (not done by
incandescent dimmers) to allow it to control fluorescent fixtures
and/or other types of reactive or capacitive loads. In a preferred
configuration, the UCD is wired in series with the fluorescent load
without observance of wiring polarity, in either the hot or return
side of the load, in a manner that is identical to a standard
single pole wall switch. In fact, the UCD is configured so as to
replace any existing wall switch to provide a dimming
functionality.
[0038] In a preferred implementation, the UCD implements an 8-bit
digital microprocessor 350 (of course, other types of
microprocessors, such as 16-bit, 32-bit, etc., may be utilized
instead of an 8-bit microprocessor, while remaining within the
scope of the invention) with embedded firmware control algorithms
for minimum parts count, and highly stable operation. The UCD is
compatible with any configuration of magnetic ballast or electronic
ballast fluorescent and/or incandescent loads. In a preferred
construction, unit size, costs, producibility, performance and
stability are optimized through the use of advanced digital and
mass production techniques. Other possible constructions of the UCD
to be described later include occupancy sensing, ambient light
correction, and AC line modem for communication with a remote
Energy Management System. All of these constructions of the UCD to
be described herein are "in series", two wire devices (see FIG. 1B
or FIG. 2).
[0039] Table 1 provides line specifications of the UCD. One of
ordinary skill in the art will recognize that other line
specification ranges may be handled by the UCD.
1TABLE 1 Line Specifications Voltage 110/277 Vac Frequency 50/60 Hz
Load Current 6.3 Amps Maximum Load/Watts 750 Watts Maximum Power
Factor 0.87-0.90 (full power) THD <35% (full power) EMI/RFI FCC
Part 18
[0040] The UCD provides AC line synchronization and timing firmware
algorithms used to provide stable dimming control of an inductive
and/or resistive and/or capacitive load without regard to applied
line voltage, frequency, and without requiring a specific
connection to the AC Line Return or Safety Ground. The UCD
implements phase control of the load, and also strategically
controls the switching element turn-on timing for stable
(non-flickering) control of inductive or resistive loads. The UCD
synchronizes on the load current zero crossing, which causes a
turning off of the series switching elements making up the solid
state switch unit 320.
[0041] Highly inductive or resistive loads, such as magnetic
fluorescent ballasts, cause a significant phase shift (delay) of
the load current waveform relative to the applied voltage waveform,
greatly complicating stable synchronization. This phase shift
varies depending on the specific installation (number of fixtures
and specific ballast specifications) as well as the selected
dimming level. As the dimming level is varied, or fluorescent tube
temperature changes, the current zero crossing synchronization
signal to the microprocessor will move significantly in real time,
causing a shift in phase timing for the next cycle. Unless a
suitable phase timing algorithm is implemented, the light fixture
will flicker in an oscillatory way, resulting in unstable (highly
unsatisfactory) dimming. It was determined by the inventors of the
UCD (the same inventors as the LCD to be described later) that
standard incandescent dimmers will not reliably function with
fluorescent or other types of reactive loads due to their
simplistic line synchronization methods. The timing correction
algorithms utilized in for the UCD are an important aspect of the
UCD design, and are described in detail below. Also, the UCD
performs well as a dimmer control with little or no flickering, for
an electronic fluorescent ballast, which is a capacitive load.
[0042] FIG. 5 shows the applied line voltage waveform, the dimmed
fluorescent load current waveform, and the microprocessor
synchronization waveform as implemented by the UCD. Also shown in
FIG. 5 are seven (7) time points in a single cycle of the applied
line voltage waveform (60 Hz or 16.67 msec time period for one
cycle), each of which is discussed in detail below. The highly
inductive nature of a fluorescent magnetic ballast causes the load
current to lag the applied line voltage, as seen in the comparison
of the AC line voltage waveform 510 with the load current waveform
520. The amount of lag depends on the circuit inductance, specific
ballast design factors, tube striking voltage which is affected by
tube temperature, and the amount of dimming phase delay being
applied by the UCD. A point by point discussion of the seven
labeled time points in FIG. 5 follows, with reference to the
circuit elements shown in FIG. 4.
[0043] Time point 1 corresponds to the rising zero crossing of the
applied line voltage waveform 510.
[0044] Time point 2 corresponds to the turn off point of Silicon
Controlled Rectifier (SCR) Q2 from the previous dim cycle. An SCR
turns off when the applied current through it reaches zero. Once
the SCR turns off, the voltage across the SCR rises sharply.
[0045] At time point 3, the turning off of SCR Q2 causes the
synchronization signal on pin 5 of the microprocessor U2 to go low,
which interrupts the microprocessor U2. In the preferred
construction of the UCD, microprocessor firmware is initialized to
only respond to the falling edge of the interrupt, and is used to
derive all phase control timing for an entire line cycle. As the
UCD dimmer potentiometer R7 is rotated clockwise, the period of
phase delay time between time point 3 and time point 4 of FIG. 5 is
increased, causing the fluorescent light fixture being controlled
by the UCD to dim. Conversely, counterclockwise rotation of the UCD
dimmer potentiometer R7 decreases this phase delay time, thereby
causing the fluorescent light fixture light output amount to
intensify.
[0046] The inventors of the UCD have found through experimentation
that a typical fluorescent tube with magnetic ballast goes off (no
light output by it) at approximately 120 degrees (about 5.5
mseconds) of phase delay. This is due to insufficient tube
ionization caused by insufficient tube heater output. Without
adequate tube ionization, the tube strike voltage exceeds that
available from the AC line. The inventors of the UCD have also
found that they were not able to visibly discern a change in light
output until the phase delay reached about 15 degrees (about 0.7
mseconds) of phase delay. The half-intensity point was about 90
degrees of phase delay (about 4.17 mseconds).
[0047] Microprocessor control of the phase delay controls the dim
level of the fluorescent fixture (the load). In response to the
falling edge of the synchronization interrupt, the microprocessor
U2 resets a free-running internal hardware timer (not shown in the
figures) to zero, then waits for the timer to reach the phase delay
value corresponding to the current position of the UCD dimmer
potentiometer R7. In a preferred implementation, the UCD dimmer
potentiometer R7 is coupled to a rotatable dial that is disposed on
a wall of a building, whereby, when a user rotates the dial, the
resistance of potentiometer R7 changes accordingly. The change in
the resistance of potentiometer R7 is discerned by the
microprocessor U2, which then computes a different phase delay
value for a next AC voltage waveform cycle based on the new dimmer
setting.
[0048] After the calculated phase delay time corresponding to time
point 4 is reached, the microprocessor U2 triggers the SCR Q1 on by
bringing pin 2 of the microprocessor U2 low for a short period of
time. In the preferred construction, an opto-isolated triac U1 is
used to trigger the SCR on while isolating the microprocessor U2
from possible damaging transients. Once the SCR Q1 is triggered on
and current begins to flow, SCR Q1 will latch itself on until
current reaches zero during the next half cycle. Current flow
through the load continues whenever the SCR Q1 or the SCR Q2 is
triggered on. When the SCR triggers on, the synchronization signal
530 goes high again. The rising edge of the synchronization signal
530 is ignored by the microprocessor U2, which only reacts to a
falling edge of the synchronization signal 530 (due to
microprocessor firmware that allows interrupts only on the falling
edge of a signal provided to its interrupt port).
[0049] Time point 5 corresponds to the next zero crossing of the
load current waveform 520. At this point, the SCR Q1 turns off.
Unlike the occurrence at time point 2, no synchronization signal
occurs at time point 5. This is because the microprocessor 5V
supply voltage (input line voltage) 340 is negative (it is a
floating supply), and the open fluorescent circuit (that is, the
load) is roughly ground. The synchronization signal 530 actually
rises slightly (few tenths of a volt) after time point 5, because
the "grounded" fluorescent circuit is actually higher in voltage
than the microprocessor negative 5V power supply 340.
Microprocessor firmware is provided such that no microprocessor
interrupt is generated from this slight perturbation of the
synchronization signal 530 (and also since it does not correspond
to a voltage drop but rather a voltage rise).
[0050] Phase control for the latter half-cycle of the AC line
voltage waveform 510 is derived from the previous earlier
half-cycle interrupt. The microprocessor U2 measures the applied
line frequency and computes the number of internal free-running
hardware timer counts that it has to wait for before triggering the
SCR on for this latter half-cycle. The timer counts for a time
period corresponding between the time between time point 5 and time
point 6.
[0051] At time point 6, the SCR Q2 is triggered on. At time point
6, the voltage of the synchronization signal 530 drops slightly (a
few tenths of a volt). No microprocessor interrupt is generated
here either, due to the microprocessor firmware being configured to
not cause an interrupt for such a small voltage drop. Again, the
SCR Q2 remains on during the negative half cycle, until the circuit
current reaches zero.
[0052] At time point 7, the rising load current waveform 520 again
reaches zero. Again the synchronization signal 530 goes to zero,
which causes a microprocessor interrupt (since it is a falling edge
of the synchronization signal 530). This also causes a
resynchronization of an internal free-running timer of the
microprocessor U2, and results in another phase delay cycle similar
to the one that was described above with respect to the time point
2 and time point 3.
[0053] The UCD hardware design according to a preferred
construction includes the components illustrated in the FIG. 4
schematic diagram. A brief description of each hardware component,
and its applied function, is provided below.
[0054] The microprocessor U2 (which corresponds to microprocessor
350 of FIG. 3) provides the control functions and algorithms for
the UCD based on an internally stored firmware program. By way of
example and not by way of limitation, in a preferred
implementation, a MICROCHIP.TM. 12C672 eight bit microprocessor
incorporates 2 kilobytes programmable read only memory (PROM) for
program storage, 128 bytes random access memory (RAM), an eight bit
timer, 4 channel 8 bit Analog to Digital (A/D) converter, 4 MHz
oscillator, and reset circuit in a very space efficient 8 pin
package. More details on this microprocessor can be found at the
Internet web site www.microchip.com. Of course, one of ordinary
skill in the art will understand that other types and sizes of
microprocessors may be utilized for the microprocessor to be used
to control the UCD.
[0055] Since the functionality of the microprocessor U2 exists
internally, in a preferred implementation, six I/O pins may be
allocated to either digital inputs and outputs or analog inputs.
Two pins are reserved for +5 volt power and ground. By way of
example and not by way of limitation, an Analog to Digital input
impedance is approximately 10K ohms.
[0056] By way of example and not by way of limitation, the "push"
on/off potentiometer switch SW1 is rated for the 6.3 ampere maximum
dimming capacity. When turned off, the dimmer/load is entirely open
circuited, resulting in no current flow to the load. Rotating
potentiometer R7 and switch SW1 are preferably integrated into a
single unit. Pushing the adjustment shaft of potentiometer R7 will
cycle switch SW1 on and off. Potentiometer R7 is wired as an
adjustable voltage divider, whereby rotating the shaft of
potentiometer R7 adjusts the voltage at pin 7 of microprocessor U2.
The microprocessor U2 reads the voltage at its pin 7 once every AC
line cycle, and uses this voltage to derive the amount of phase
delay (dim level) for the load. Resistor R8 is wired between the
potentiometer wiper and ground, and is used to provide a more
linear relationship between the potentiometer position and
resulting dim level. By way of example and not by way of
limitation, resistor R8 has a resistance of 4.7 kohms.
[0057] In the preferred implementation of the UCD, two SCRs Q1, Q2
are connected back to back to provide an active switching element
for the UCD, and correspond to the solid state switch 320 of FIG.
3. The inventors of the UCD found that TRIAC devices do not trigger
as accurately as back-to-back SCRs when switching a highly
inductive resistive load. Consistent and accurate switching element
turn-OFF at the current zero crossing is very important to line
synchronization. The use of a TRIAC as the active element may
result in occasional flickering, which may be due to an unstable
holding current level. As a result, the inventors found that an
active element that includes back-to-back SCRs functions much
better than one having a TRIAC in the energy savings device
according to the invention, whereby using two SCRs provides an
increase in switching current capability and better heat
distribution to a heat sink.
[0058] By way of example and not by way of limitation, the SCRs
utilized in a preferred implementation of the UCD are 600V, 15
ampere devices. The SCRs Q1, Q2 are designed to run very cool at
maximum specified loads. The choice of which type of SCRs to use in
the UCD may also be made based on a low holding current parameter
for the SCRs. When a signal of either polarity triggers the
opto-isolated triac U1, positive pulses from pin 4 and from pin 6
of the opto-isolated triac U1 are transmitted to gates (G) of the
SCRs Q1, Q2, respectively. Opto-isolated triac U1 of FIG. 4
corresponds to solid state driver unit 330 shown in FIG. 3.
[0059] SCRs conduct current in one direction (from anode to
cathode), with back-to-back SCRs having the capability to conduct
in both directions. SCRs are latching devices, meaning that once
they are trigger on, they will continue conducting until the
anode-to-cathode current through them reaches zero (or reverses
direction). An SCR is triggered on by pulling current out of its
Gate pin, or bringing the Gate voltage a few volts lower than its
anode, pin. The holding current specification for an SCR specifies
the minimum SCR current necessary for the SCR to latch on, and to
remain latched on. A holding current on the order to 20
milliamperes is needed for proper operation of a typical SCR. Once
the SCR current drops below the specified holding current, it will
turn off until retriggered again. Only the SCR with its anode
voltage positive relative to its cathode voltage is capable of
being triggered on. This means that SCR Q1 controls the load during
the positive half of the AC voltage waveform cycle, and SCR Q2
controls the load during the negative half of the AC voltage
waveform cycle.
[0060] As shown best in FIG. 4, the opto-isolated triac U1 is used
to trigger the SCRs Q1, Q2. The microprocessor U2 triggers
opto-isolated triac's U1 internal triac, and subsequently one or
the other SCR Q1, Q2, by illuminating the opto-isolated triac's U1
internal light emitting diode (LED). LED illumination occurs when
the microprocessor U2 pulls its output pin 2 low, resulting in LED
forward current. The opto-isolated triac U1 is capable of
conducting current in either direction, depending on the relative
voltages of pins 4 and pin 6 of the opto-isolated triac U1. For
example, if pin 6 is higher than pin 4 of the opto-isolated triac
U1, current will flow from pin 6 to pin 4. Connecting the
opto-isolated triac U1 between the gates of the two SCRs Q1, Q2
provides a convenient method of triggering back-to-back SCRs.
[0061] Current flows into pin 6 of the opto-isolated triac U1 and
out pin 4 in response to the positive half of the AC sine wave
voltage waveform 510 (see FIG. 5) and vice versa in response to the
negative half of the AC sine wave voltage waveform 510. Pulling
current out of the associated SCR gate turns the device on. The
internal structure of the SCR allows current to flow into the gate
of the opposite device without triggering the device. Therefore,
SCR Q1 will remain latched through the positive half of the sine
wave current, whereupon at approximately zero crossing, the
latching current will be insufficient and SCR Q1 will switch off.
Similarly, the gate of SCR Q2 will source current into pin 4 of the
triac U1 and out pin 6 of the triac U1 during negative half of the
AC cycle, and remains latched again until approximately zero
crossing. This switching sequence repeats for each cycle of the AC
sine wave voltage waveform 510, providing full power of sine wave
current to the (fluorescent) load. Accurate and stable triggering
of the SCRs Q1 and Q2 are very important to the suppression of
flickering.
[0062] Back-to-back SCRs are used to form an active element of an
energy savings device according to a preferred implementation of
the UCD since they were found by the inventors of the UCD to be
somewhat more stable in their turn OFF characteristics than a
TRIAC. In order for an SCR to latch on, the anode/cathode current
must exceed the latching current requirement. Once it is latched
on, an SCR will remain on until it is turned off when anode/cathode
current drops below holding current requirement. With such
features, SCRs are ideal devices to be utilized for the active
element that corresponds to the solid state switch 320 (see FIG. 3)
of the UCD. One of ordinary skill in the art will recognize that
other types of solid state switches may be utilized, as well as
switch drivers, beyond the ones described herein.
[0063] In the preferred implementation of the UCD, the
opto-isolated triac U1 is utilized to provide driving signals to
the SCRs Q1, Q2. By way of example and not by way of limitation,
the opto-isolated triac U1 may be a MOC3022 opto-isolated triac,
which drives the Q1 and Q2 gates and provides line transient
protection to the microprocessor U2. A LED drive current of
approximately 5 milliamps (via resistor R6, which is a 620 ohm
resistor in the preferred implementation) is sufficient to reliably
trigger the opto-isolated triac U1. The GP5 pin of microprocessor
U2, which corresponds to pin 2 of the microprocessor U2, is
configured for output and is capable of sinking up to 20
milliamps.
[0064] Referring to FIG. 5, the opto-isolated triac U1 outputs a
drive signal starting at time point 6, whereby the drive signal is
turned off well before the load current zero crossing at time point
7. Also, the opto-isolated triac U1 outputs a drive signal starting
at time point 4, whereby the drive signal is turned off well before
the load current zero crossing at time point 5.
[0065] Referring to FIG. 4, resistor R2 is a current limiting
resistor, and is provided so as to limit the series current of the
opto-isolated triac U1 to be less than one ampere under all
circumstances. For 277 VAC installations, the value of resistor R2
should preferably be increased to 470 ohms due to the increase in
the AC waveform voltage level.
[0066] In a preferred implementation of the UCD, the SCR trigger
signal output by the optoisolated triac U1 stays on for
approximately 1.2 milliseconds. The actual SCR trigger signal on
time is not critical, since an SCR triggers on within a few
microseconds of receiving a trigger signal to its gate. In a
preferred implementation of the UCD, and as explained above, the
SCR trigger signal turns off before the next zero crossing of the
load current waveform, in order to enforce some SCR off time (e.g.,
0.25 milliseconds). This off time is provided in order to recharge
the 5 volt power supply 340 (see FIG. 3) for the next cycle.
[0067] Resistor R1, capacitors C1, C2, diodes D1 and D2, and the 5
volt power supply of FIG. 4 are all utilized for a power supply
control for the UCD, and together form the power supply unit 340
shown in FIG. 3. In a preferred implementation of the UCD, the 5
Volt power supply 340 provides up to 20 millamps of power to the
microprocessor U2, opto-isolated triac U1, and the potentiometer R7
at all times in which the UCD is powered. The 5 Volt power supply
340 floats with the AC line input. Voltage is derived by the widely
varying voltage across SCRs Q1 and Q2. Power is available to the
circuit only when SCRs Q1 and Q2 are switched OFF. When SCRs Q1 and
Q2 are turned on, the 5 Volt supply 340 is maintained by capacitor
C1 and is stabilized by zener diode D1. Silicon Diode D2 provides a
discharge path for capacitor C1.
[0068] Resistor R1 and capacitor C2 provide an AC coupled voltage
drop to limit silicon diode D1 and zener diode D2 current and
dissipation. By way of example and not by way of limitation, the
microprocessor U2 remains entirely functional with any supply
voltage over 3.3 Volts at a current of 3 milliamps. In a preferred
implementation of the UCD, supply regulation is not critical as
long as the supply voltage maintains the 3.3V minimum.
[0069] Resistors R3, R2, R4, R5, and diode D3 of FIG. 4 are
elements making up the Line sync unit 360 shown in FIG. 3. The
falling half of the AC line output (when SCRs Q1 and Q2 turn off)
is used for line synchronization. SCRs Q1 and Q2 turn off at the
line current zero crossing. Zener diode D3 protects the
microprocessor interrupt input (port 5 of the microprocessor U2)
against unforeseen line and switching transient spikes. Resistor R5
limits current input to the microprocessor U2 and allows the
internal microprocessor protection or clamp diodes to function
while preventing any possible burnout. Resistors R2, R3 and R4 also
provide a current limiting and line synchronization function for
the UCD.
[0070] The inventors of the UCD have realized that stable AC line
synchronization is very important to non-flickering operation when
controlling inductive and/or resistive loads (especially
conventional Magnetic Ballast Fluorescent Fixtures), and even for
controlling capacitive loads (such as Electronic Ballast
Fluorescent Fixtures). These synchronization methods are
implemented in the firmware of the microprocessor U2 used in the
UCD.
[0071] The microprocessor firmware provides a Line Sync Edge
Detection function. In detail, the microprocessor U2 is interrupted
on the falling edge of Line Syncronization signal 530 (see FIG. 5)
which occurs once every AC cycle as the switching element turns off
at the current zero crossing. SCRs have a characteristic in that
they latch themselves on until the current through them reaches
zero. The point where they turn off is used as the line
synchronization. An internal timer of microprocessor U2 is
initialized at this interrupt, and timing parameters for the next
entire AC cycle calculated in firmware. Using a single current zero
crossing per AC cycle cancels any non-uniformity of the positive
and negative halves of the current waveform, as well as eliminates
interrupt input threshold hysteresis effects.
[0072] The firmware of microprocessor U2 also provides an AC Line
Period Determination function. In detail, at initial power up, the
microprocessor performs a timing analysis of the AC line with the
load switched off so that specific timer counts for each half phase
may be calculated. Leaving the load off during this period provides
a very accurate measurement of the AC line voltage, without
inductive load phase shift influence. At the first interrupt after
initial power up, the microprocessor timer is initialized to zero.
At the next interrupt the timer value is stored, representing the
number of timer counts for a full AC cycle. Subsequent phase timing
parameters are derived from this number. Intra-interrupt timing
functions are driven by waiting for specific timer counts.
[0073] The microprocessor firmware also performs a Phase Timing
Calculation function. In detail, once the line period has been
determined, the firmware of microprocessor U2 performs phase timing
calculations. Since synchronization is performed only once per AC
cycle, a determination of the cycle half time is made by dividing
the period by two (shift right one time). Next, a calculation of
when the cycle is completed (cyclendtime) in anticipation of the
next interrupt is made.
[0074] The firmware of microprocessor U2 further performs a Dead
Time Implementation function. In detail, circuit power is only
available when the series switching elements (SCRs) are turned off,
therefore microprocessor firmware guarantees a minimum off time
(deadtime) for each AC line half cycle to restore the 5 volt
supply.
[0075] The firmware of microprocessor U2 also performs a Fixture
Warmup function. In detail, fluorescent tubes should be fully
warmed up before they can be reliably dimmed. This feature may not
be desirable for other types of inductive or resistive loads, and
may be easily deleted from the control device, without departing
from the scope of the invention. To address this requirement, the
fixture is set to full intensity for a first time period after
initial power up. By way of example and not by way of limitation,
the first time period is set to 12 seconds. Upon completion of the
12 second period, the intensity is returned to the dim level
corresponding to the position of potentiometer R7 (see FIG. 4).
[0076] : The firmware of microprocessor U2 further provides a Sync
Window Implementation function. In detail, in order to reject
spurious line transients which could possibly upset dimmer timing,
a sync window algorithm is utilized in the first embodiment. At the
end of each full AC cycle, the microprocessor U2 waits until
cyclendtime which occurs a few timer counts before the next line
interrupt, before re-enabling interrupts. If a spurious interrupt
occurred between the last sync edge and cyclendtime, it is
effectively ignored.
[0077] The firmware of microprocessor U2 also provides a Slow Phase
Timing (Dim Level) Changes function. In detail, when using a
current zero crossing sync with an inductive magnetic ballast, any
phase timing (dim level) change causes a slight synchronization
variance which could cause instability (flickering) if not greatly
damped out. To greatly lessen this possibility, phase timing
changes are limited to one timer count per AC cycle, thereby
minimizing this effect.
[0078] The firmware of microprocessor U2 further provides a
function for pulsing the SCRs ON at the correct time. In detail,
the SCRs Q1, Q2 are pulsed on, instead of just turned on and left
on at the proper time, to reduce the drain on the 5 Volt power
supply 340 (see FIG. 3).
[0079] More details of the microprocessor firmware implementation
according to a preferred implementation of the UCD is provided in
detail below. In the preferred implementation of the UCD, the
firmware of microprocessor U2 is written using a Microchip
assembler language specific to the 12C672 eight bit microprocessor.
Of course, based on the type of microprocessor utilized in the
first embodiment, the choice of software language used to write the
microprocessor firmware will be utilized accordingly.
[0080] A detailed flow chart of the preferred implementation of
microprocessor firmware to be utilized by a microprocessor U2
provided in the UCD is illustrated in FIG. 6. Major flow chart
function descriptions are provided below.
[0081] For UCD implementation, a Reset occurs only during initial
power up. At this time, microprocessor memory and register contents
are random, and are thereby initialized before they can be used. In
the preferred implementation of the UCD, the microprocessor U2 has
an internal reset circuit which recognizes when power is initially
applied. Upon Reset, the microprocessor U2 begins execution at
address 0000, which is where the initialization firmware starts.
Once this initialization executes, it is not re-executed unless
another power up sequence occurs.
[0082] Two interrupts are enabled for the UCD according to a
preferred construction. First, the external synchronization falling
edge interrupt, from which all phase delay calculations are
derived, is enabled. Second, the internal hardware free-running
timer overflow interrupt is enabled. In the preferred
implementation of the first embodiment, the timer is an 8 bit timer
which is incremented once every 64 microseconds. The timer
overflows every 16.384 milliseconds (256 counts), which is slightly
less than a full 16.667 millisecond line-cycle. During an
interrupt, the microprocessor U2 stops executing where it is, saves
it's state (e.g., processor status word and program counter), and
executes interrupt code. Initial line parameter calculations,
hardware timer maintenance, and Analog to Digital Converter (ADC)
maintenance occurs during the interrupt firmware.
[0083] Referring to FIG. 6, "Main" is the start of the primary UCD
software program run by the microprocessor U2. It is entered after
initial power up initialization and once per complete line cycle.
"Main" keeps track of the current line half cycle, and performs all
phase timing calculations based on the free-running hardware timer.
Phase timing is implemented by waiting for the appropriate
free-running timer count to occur, then calling the TrigScr
subroutine which implements the SCR trigger timing. Specific
free-running timer values to wait for are calculated based on the
following factors:
[0084] a) Dimpot position: As indicated by the converted ADC value.
Rotating the dimpot potentiometer clockwise will reduce phase
delay, and increase florescent intensity.
[0085] b) FullOnMode: During the first 12 seconds after initial
power up, the UCD is in FullOnMode. During this time, the
florescent load is forced into full intensity to warm the tubes.
During FullOnMode, phase delay is fixed at the constant value
fulltime. When not in FullOnMode, phase delay is calculated based
on dimpot position, and results of the softdim calculation. The
softdim calculation prevents large cycle to cycle phase delays from
occurring. This provides a stabilizing effect on florescent
intensity.
[0086] C) Cycle Half: After completion of the first half of the
line cycle, firmware waits for the pre-calculated half period
free-running hardware timer value, resets the timer, and jumps back
to Main. This causes the second half cycle phase delay timing to be
identical to the first half cycle. At the end of the second half
cycle, firmware will wait for the free-running hardware timer to
reach the pre-calculated cyclendtime, then re-enable interrupts in
anticipation of the next full line cycle.
[0087] After the appropriate phase delay has be determined, a call
to TrigScr is executed whereby the SCRs Q1, Q2 are turned on at the
appropriate times.
[0088] The TrigSCR sub-routine toggles the SCRs Q1, Q2 on and off
for a period of time to minimize drain on the 5V power supply. Once
the SCR current is greater than the SCR specified holding current,
it will latch on for the duration of the half cycle, until the
current reaches zero again. Relative free-running hardware timer
values are used to accomplish this pulse ON, pulse OFF, and pulse
duration timing.
[0089] The following are descriptions of each section of the dimmer
firmware utilized by the microprocessor U2 according to a preferred
implementation of the UCD, whereby each section is identified by
line number, then label and references to the flow chart of FIG. 6.
Of course, other firmware may be utilized as would be recognized by
one of ordinary skill in the art.
[0090] Line 1: Defines the microprocessor as the target for the
assembler
[0091] Line 2: This include file defines the microprocessor
register names and memory mapped register addresses.
[0092] Line 5: A list of defined memory mapped addresses
follows:
[0093] dimpot: Storage of the dim potentiometer analog value
[0094] timerstat: Mode Flags specific to dimming mode
[0095] tmrovflcntr: Used as an overflow counter to the internal 8
bit counter TMR0
[0096] intovflcntr; LSB of counter used for 12 sec full ON
[0097] fullintcntr: MSB of counter used for 12 sec full ON
[0098] timereg: Temp Storage of TMR0 Count
[0099] periodmsb: Measured MSB of Full wave. TMR0 Count
[0100] periodlsb: Measured LSB of Full wave TMR0 Count
[0101] halftime: Calculated TMR0 Count for Half Wave
[0102] trigtime: Calculated TMR0 Count to Trigger SCR
[0103] SCRofftime: Temp Storage where time to turn off SCR is
stored each cycle
[0104] SCR1stime: Temp Storage for Last SCR time . . . subse quent
SCR ON/OFF functions key off of this stored TMR0 value
[0105] cycendtime: Re-Enable Edge Interrupt time
[0106] softlast: Temp Storage of last dim time count is stored.
Used for Soft Dim.
[0107] Line 23 ;GPIO Bit Defs
[0108] potanal 12C672 GPIO Pin Allocated to Potentiometer Analog
Input
[0109] gp1 12C672 GPIO Pin Not Used
[0110] acint 12C672 GPIO Pin Allocated for AC Interrupt Input
[0111] gp3 12C672 GPIO Pin Not Used
[0112] gp4 12C672 GPIO Pin Not Used
[0113] SCRdrv 12C672 GPIO Pin GPIO SCR Drive Output.
[0114] Line 31 ;TimerStat Bit Defs
[0115] firstedg Flag: First Interrupt Edge Occured
[0116] secedge Flag: Second Interrupt Edge Occured
[0117] fullonmode Flag: Full on mode
[0118] newedge Flag: New Edge Flag
[0119] cycsechalf Flag: Second Half of Period
[0120] oddedge Not Used in this Version.
[0121] Line 39 ;Value Defs
[0122] intovflow=d`3` ;FullOnMode Int Overflows 4Secs per inc
[0123] dimofst=h`4` ;ADC Offset, Higher Numbers go Dimmer
[0124] maxofst=h`7f` ;Maxdim Offset
[0125] maxdima=h`fe` ;Maxdim Level
[0126] maxdimlyl=h`d0` ;Maxdim
[0127] intwindow=d`3` ;Interrupt Window
[0128] SCRpulsetime=h`37` ;Time SCR is Pulsed ON and Off
[0129] deadtime=d`8` ;Dead time past zero crossing
[0130] fulltime=d`8` ;Full On time past zero crossing.
[0131] Line 54 rstvec The microprocessor starts execution at
address 0 after Reset, Interrupts are disabled, then memory
initialized.
[0132] Line 58 intvec The microprocessor interrupt vector for
enabled interrupts is at address 4.
[0133] Line 59 intsvc TMR0 is cleared at each falling edge of the
AC interrupt. After a Reset, a wait for the zeroth edge is
executed. Upon occurrence of the zeroth edge, TMR0 overflow
interrupt is enabled so that the AC edge to edge period can be
calculated. Upon occurrence of the first edge interrupt, AC
parameters are calculated and used in subsequent phase
calculations.
[0134] Line 61 Jump table based on edge occurrences.
[0135] Line 65 notfirst Zeroth edge interrupt has occurred, enable
TMR0 overflow Interrupts.
[0136] Line 72 firsthap First interrupt has happened, count number
of TMR0 overflows, enable Next TMR0 overflow interrupt.
[0137] Line 78 notmrint If it's a second edge interrupt, then
disable subsequent TMR0 overflow Interrupts, and then calculate AC
timing parameters.
[0138] Line 81 caltime AC parameters such as period, halftime, and
cyclendtime, are calculated once. Flag secedge is then set, and
further edge interrupts enabled. From now on, each edge interrupt
constitutes an AC line synchronization signal used for phase
control of the SCRs.
[0139] Line 100 sechap Once the second edge interrupt has occurred,
then 12 seconds of full on is executed to fully warm,the tube
heaters. Fullintcntr, and intovflcntr form a 16 bit counter which
count 16.667 mS edge interrupts. A total of 768 edge interrupts
provides a net 12.8 seconds of fluorescent tube full on time.
[0140] Line 112 fulldun Upon conclusion of the full on mode, the
fullonmode flag is cleared in timerstat.
[0141] Line 113 notfull Each edge interrupt, the A/D converter is
checked for conversion complete. If it has completed the dimpot
value is inverted by exclusive Oring the input value and stored in
the memory location dimpot.
[0142] Line 121 nocvrt A/D conversion has completed, another
conversion is started. The newedge flag is set and the cycsechalf
flag cleared, indicating to the main program code that an interrupt
had occurred, and that it is now the first half of the AC
cycle.
[0143] Line 123 glitint TMR0 is cleared, Edge interrupts are
re-enabled, and a return from interrupt executed.
[0144] Line 129 initmem Microprocessor hardware registers are
initialized, program defined registers are cleared, and finally
edge interrupts are enabled.
[0145] Line 173 main Main part of the program. Wait for second edge
interrupt. At this time, all AC line parameters have been
calculated, and normal phase control can commence.
[0146] Line 175 main1 Wait for each new edge. Newedge is a
handshake flag with intsvc which is used to wait for a new edge at
the completion of each AC cycle.
[0147] Line 178 main2 Entered at the start of each AC cycle.
Potentiometer scaling to actual TMR0 counts are performed once per
AC cycle. Edge Interrupts are disabled, dimpot contains the
commanded dim value. The memory location softlast is used to
calculate the desired dim value time.
[0148] Line 189 sechalf This is the entry point for the second half
of the AC cycle. If NOT in Fullonmode, then go to dimtrig. Else, it
is fullonriode at sechala.
[0149] Line 191 secala A wait until TMR0=deadtime is executed.
Deadtime defines the earliest time (in TMR0 counts) the SCR may be
triggered ON after an AC line voltage zero crossing. A call to
trigSCR turns the SCR on for a period of time. After returning, the
first cycle half is complete.
[0150] Line 198 dimtrig Fullonmode has completed, enforce minimum
deadtime limit, by waiting for TMRO to reach deadtime value.
[0151] Line 202 dimwait Past deadtime, now wait for the calculated
TMR0 value corresponding to the calculated phase delay for the
indicated dim level. The memory location trigtime is incremented or
decremented once each time, effectively "chasing" the desired dim
level stored in softlast.
[0152] Line 217 hafcycl Halfcycle parameters are checked. If
already in the second half, a wait for next edge interrupt (jump to
rstcycle) is executed. If Not already in second half, a wait until
the previously calculated Halftime TMR0 value is executed. Once
past halftime, TMR0 is cleared, and the cycsechalf flag is set.
Then a jump to sechalf occurs, duplicating timing parameters for
the second half of the AC cycle.
[0153] Line 229 rstcycle Once timing for the second half of the AC
cycle has been executed, a wait until cyclendtime is executed
before edge interrupts are Re-enabled. This provides a window which
rejects AC line transients which occur outside of the window. Upon
passage of the window, Interrupts are re-enabled, and a jump to
main1 is executed, causing a Wait for the next edge interrupt.
[0154] Line 240 trigSCR TrigSCR is a routine that is called when
it's time to turn on the SCR. When called, the SCR is triggered on
(SCRdrv is brought low), then the SCRofftime is calculated based on
addition of the constant SCRpulsetime, and the current TMR0 value.
A wait until SCRofftime is executed, whereupon the SCR is turned
off (SCRdrv is brought high). If cycendtime occurs during the time
trigSCR executes, drive to the SCR is deasserted, and a return to
the calling code is executed.
[0155] Line 265 end End of the program.
[0156] FIG. 7 shows a block diagram of an energy savings device
UCD-2 according to a different construction, and FIG. 8 shows a
schematic circuit diagram of the energy savings device UCD-2
according to that different construction. The energy savings device
UCD-2 provides all of the functions of the UCD described
previously, along with extra functions. The UCD-2 includes an
occupancy sensor, an ambient light sensor, and an AC line modem for
remote communications to a central energy management system, for
example. The UCD-2 provides a more robust energy savings function
than the UCD described previously.
[0157] As shown in FIG. 7, an ambient light sensor unit 710 of the
UCD-2 provides the capability to adjust the dimming level for
constant level illumination during day/night ambient illumination
variances. Referring also to FIG. 8, the ambient light sensor unit
710 includes a photo-resistor R19 with amplifier 720, which
provides a stable indication of the total ambient illumination via
a signal AMBLITE provided to port 1 of the microprocessor U2. The
microprocessor U2 adjusts the dimming level to maintain this total
ambient illumination level. For example, during a cloudy day, if
the clouds break during the afternoon and thus the light through
windows of an office increases, this results in an increase in the
illumination level picked up by the ambient light sensor unit 710.
Accordingly, the microprocessor U2 will adjust the load current
waveform to provide a slightly dimmer signal than what was
previously provided (during the cloudy period), so as to maintain a
stable ambient illumination for the office.
[0158] Referring to FIG. 7, the occupancy sensor unit 730 of the
UCD-2 provides the capability to sense movement within an
illumination area. The occupancy sensor unit 730 is configured to
provide a signal indicative of no movement to the microprocessor U2
if no movement is sensed after an extended interval of time (e.g.,
15 minutes or more). Upon receipt of the "no movement" signal from
the occupancy sensor unit 730, the microprocessor U2 turns the
light fixture off, in order to save energy. Similarly, illumination
to a preset level is restored if movement occurs, such as when a
person walks into a room. Referring to FIG. 8, the occupancy sensor
unit 730 according to a preferred implementation includes a passive
infrared sensor 750 with a multifaceted (Fresnel) lens 740 in front
of a pyroelectric transducer. For example, a Murata IRA-E710ST0 may
be utilized as the motion detector for the occupancy sensor unit
730. The lens 740 focuses infrared energy from a multitude of
narrow, discrete beams or cones. As a warm body moves across the
field of view of the detector, the transducer output has peaks and
valleys which are amplified, thereby providing an indication that
movement is occurring. This results in a signal MOTDET that is
indicative of movement being provided to the microprocessor U2.
[0159] Referring to FIG. 7, the AC line modem 760 of the UCD-2
enables bi-directional communications with an energy management
unit, such as with a centralized energy management system (EMS). In
one implementation shown in FIG. 8, the AC line modem is
implemented as a line modem TDA5051 component. The EMS has the
capability to remotely control some or all dimming functions and
modes including turn off illumination (via signal PWRDWN provided
to microprocessor U2), set dimming level, and verify occupancy
sensor status (possible burglar alarm function). The EMS is
preferably a standard personal computer with external AC line modem
connected to a serial port. Software running under an operating
system, such as the Windows.TM. operating system, maintains the
status of all units within a local area. The AC line modem 760
functions by modulating a 200 KHz signal onto the AC power line via
a filter network 770 that includes an inductor L1 and a capacitor
C4 (see FIG. 8), in one possible implementation of the UCD-2. The
EMS can communicate with a wide area of dimming units that are on a
common AC line step down transformer, for example. Each dimming
unit carries a unique address to facilitate a multi-drop
communications network via the power lines.
[0160] In a third possible construction of the UCD, unlike the
"loaded" UCD-2, only the ambient light sensor unit of the UCD-2 is
provided along with the features of the UCD.
[0161] In a fourth possible construction of the UCD, only the
occupancy sensor unit of the UCD-2 is provided along with the
features of the UCD.
[0162] In a fifth possible construction of the UCD, only the AC
line modem of the UCD-2 is provided along with the features of the
UCD. In another possible implementation, both the occupancy sensor
unit and the AC line modem (but not the ambient light sensor) of
the UCD-2 are utilized along with the features of the UCD. In yet
another possible implementation, both the AC line modem and the
ambient light sensor (but not the occupancy sensor unit) are
utilized along with the features of the UCD. In still yet another
possible implementation, both the occupancy sensor unit and the
ambient light sensor (but not the AC line modem) are utilized along
with the features of the UCD.
[0163] A sixth possible implementation includes all of the features
described above with respect to the UCD-2, as well as a remote
control function. The remote control function allows a user to set
a light level by a remote control unit, without having to go to a
switch box on a wall. By pointing the remote control unit in a
direction of the switch box, and by enabling a button on the remote
control unit, a signal is picked up by an element (e.g., infrared
sensor, IR sensor) on the switch box, similar to a television
remote control unit, whereby a room light level is either increased
or decreased depending on the user's selection on the remote
control unit. The remote control function can also be used with any
of the other implementations (or constructions) described
above.
[0164] A seventh possible implementation of the UCD is described
herein with respect to FIGS. 9 and 10. The seventh construction of
the UCD is directed to a master/follower control system, whereby a
master unit controls one or more reactive loads, and whereby at
least one follower unit coupled to the master unit responds exactly
the same as the master unit to control loads coupled to each
follower unit. The master/follower control system provides for
modular flexibility for different sizes of facilities. FIG. 9 shows
a schematic circuit diagram of a master unit 900. FIG. 10 shows a
schematic circuit diagram of a follower unit 1000 that is
controlled by the master unit 900 of FIG. 9.
[0165] The seventh possible construction of the UCD includes a
conduction angle phase switching circuit connected in parallel with
a reactive load, an AC power source for switching power across the
load, and a line switching circuit for enabling the application of
AC power to the load through the phase switching circuit.
[0166] In the seventh construction of the UCD, an ambient light
sensor 910 is provided for generating a light control signal
indicative of the amount of ambient light present in a particular
location. Coupled to the light sensing circuit is a phase angle
conduction control circuit, which generates and applies to a
control terminal of the phase switching circuit a phase control
signal to control the phase angle conduction time of the phase
switching circuit, based on the amount of ambient light measured by
the light sensing circuit, in order to maintain a substantially
constant lighting level. In FIG. 9, the microprocessor U3 functions
as the phase angle conduction control circuit.
[0167] Integrated with the phase angle conduction control circuit
is an RC filter circuit which gradually increases the phase angle
conduction time switching circuit from zero, or from a
predetermined minimum value, to a steady state phase angle
conduction time based on the ambient light conditions sensed by the
light sensing circuit, after power enabling by the line switching
circuit.
[0168] Referring to FIG. 9, the master unit includes a line switch
SW1 connected in series with an AC power source between a hot
(black) and a neutral (white) power line. Connected in series
between the hot and neutral power lines is an reactive load (e.g.,
fluorescent lamp), and a phase angle control switching device that
includes SCRs Q1 and Q2 and an opto-isolated triac U1 for driving
the SCRs (see discussion with respect to the first embodiment).
[0169] Also shown in FIG. 9 is the microprocessor U3, which
receives a line sync signal from a bridge circuit D1 that is
coupled to the hot and neutral lines. Based on the line sync
signal, and based on the setting of the potentiometer and switch
SW1, the microprocessor U3 provides control signals to the
opto-isolated triac U1, as well as to follower units coupled to the
master unit via pulse width modulated (PWM) signaling.
[0170] FIG. 10 shows the elements of a follower unit 1000, which
receives the PWM control signals from the master unit, and which
controls one or more loads connected to the follower unit based on
on/off switching of its active element (SCRs Q1, Q2, and
opto-isolated triac U1) via those control signals.
[0171] A first embodiment of the invention will be described below,
which utilizes a linear control device (LCD) to control a load such
as a fluorescent light fixture, with reference to FIGS. 11, 12A,
12B, 12C, and 13. The LCD is an improvement on the various
constructions of the UCD described previously.
[0172] The LCD encompasses both center switched phase control and
closed loop linear current control dimming. FIG. 11 illustrates a
preferred implementation of the LCD according to the first
embodiment. The LCD 1100 includes a bridge rectifier 1110 on the
output that allows the use of a single switching/linear control
element 1120 to control current flow during both halves of the AC
cycle of an AC voltage waveform. By way of example and not by way
of limitation, the switching/linear control element 1120 may be a
MOSFET, an IGBT, or a BJT. Without the bridge rectifier 1110, two
control elements with a relatively complex biasing arrangement
would be required, as described above with respect to the first and
second constructions of the UCD described previously.
[0173] For the purposes of description of the operation of the LCD,
assume the use of a MOSFET as the switching linear control element
1120, although an IGBT or BJT device can be utilized as described
above with only minor circuit changes. Selection of a particular
device for the switching linear control element 1120 could be
based, for example, on cost, available device specifications
(primarily RdsON for MOSFETs and VceSat for IGBT and BJT), load
characteristics and resulting thermal considerations. Any of these
devices allow switching fully On or OFF at any time during the AC
cycle or linearly controlling load current.
[0174] As shown in FIG. 11, the LCD 1100 also includes a processor
1130, a dim level setting element 1140, a low pass filter 1150, an
operational amplifier 1160, and a floating power supply 1170. The
bridge rectifier 1110 is disposed between the line 1175 (that
provides the AC input voltage waveform) and the load 1185. The
processor 1130 provides control of the MOSFET 1120, whereby a 5V
switch control output voltage on line 1188 turns the MOSFET 1120
OFF, a 0 V switch control output voltage on line 1188 turns the
MOSFET 1120 ON, and a tristate output on the line 1188 corresponds
to a linear current control mode.
[0175] The pulse width modulated (PWM) output on line 1192 of the
processor 1130 is either a 0% duty cycle corresponding to a 0V
output on line 1192, a 100% duty cycle corresponding to a 5V output
on line 1192, or a 50% duty cycle corresponding to a 2.5V output on
line 1192.
[0176] A voltage line synchronization signal on line 1194 is input
to a Timer Reset input of the processor 1130, where the digital
voltage line synchronization waveform 1196 and the Applied AC
Voltage waveform 1198 (input by way of the line 1175) are shown.
The commanded dim level that a user sets by way of the dim level
setting element is inputted to an analog input 1177 of the
processor 1130.
[0177] Note that, as shown in FIG. 11, the LCD 1100 is connected in
series with the load 1185, with no neural or ground wire connection
to the LCD 1100.
[0178] FIG. 12A illustrates the LCD center switching concept. In
FIG. 12A, progressively narrower load current pulses 1220A, 1220B,
1220C, 1220D, 1220E corresponding to increased dimming levels are
applied to the MOSFET 1120, whereby each pulse is centered at a
peak of the Applied AC voltage waveform 1198. The times when the
pulses 1220A, 1220B, 1220C, 1220D and 1220E are provided correspond
to ON periods of the output AC voltage waveform, and all other
times correspond to OFF periods of the output AC voltage
waveform.
[0179] By center-switching the MOSFET 1120 around the peak of the
applied AC voltage waveform 1198, inductive load current will
increase quicker, reach higher magnitudes, and minimize the
resulting voltage to load current phase shift (lower power factor).
Additionally, center switching of the applied AC voltage waveform
1198 maximizes magnetic ballast secondary voltages, increasing the
probability of firing the fluorescent tube. Also, instantaneous
fluorescent tube heater current (and instantaneous temperature) is
maximized during this center switched ON period when the applied
voltage and resulting current is highest. MOSFET gate-source
voltage (Vgs) is positive (e.g., 10 volts or more) to turn the
MOSFET 1120 fully ON, zero volts to turn the MOSFET 1120 fully OFF,
and somewhere in between to cause it to become a linear (resistive)
control element.
[0180] FIG. 12B illustrates the linear current control mode of the
LCD 1100. When biased fully ON, the RdsON specification of the
MOSFET 1120 determines it's effective series resistance. Current
MOSFET technology has developed inexpensive 600 Volt devices with
RdsON specifications of less than 0.2 ohms, suitable for
controlling 500 Watt or more inductive loads when placed in a
standard Wall Switch electrical enclosure. Lower voltage devices
can be made with lower. RdsON specifications. Typically, half the
voltage rating results in a device with one fourth the RdsON
specification. Heat generated within the MOSFET 1120 obeys Ohm's
I.sup.2R law for the duration of time it's conducting power. Low
dimming levels are achieved by controlling the period of time the
MOSFET 1120 is fully ON, centered around the peak of the applied AC
voltage waveform 1198.
[0181] Current through an inductive load builds/decays slowly, and
if the conduction width is too constrained (narrow), very little
current will develop before the switch is turned OFF. Referring now
to FIG. 12B, which shows progressively narrower load current pulses
1240A, 1240B, 1240C, 1240D, and 1240E, whereby linear load current
limiting is performed at some point while the dimming level is
increased, if linear current control was not performed, the center
switched load current width would become too narrow for adequate
load current to develop through an inductive load, thereby
resulting in the fluorescent light extinguishing. Before this point
occurs, the LCD 1100 will maintain the adequate center switched
load current width (in FIG. 12B, the pulses 1240C, 1240D and 1240E
are maintained at a minimum allowed current width even though the
dimming level is increased), then revert to closed loop Linear
Current control to achieve the additional stable dimming.
[0182] When switched ON or OFF, the resulting heat generated within
the MOSFET 1120 is relatively low (determined by the load current
and RdsON of the device), while when being used as a linear control
device, the heat generated will be significantly increased
(Vdrain-Vsource times the load current). However, since the LCD
1100 uses high efficiency ON/OFF switching for the majority of the
dimming, and linear current control mode only for the remaining
very short period of time at high dimming levels, MOSFET linear
mode heat is minimized. Thus, by using both timed center switched
phase control, augmented with a linear current control technique at
high dimming levels, very stable, effective and thermally efficient
dimming of fluorescent light fixtures is achieved.
[0183] As compared to the UCD or the UCD-2 or the other
constructions of the UCD described previously, the use of a Triac
or back-to-back Thyristors for the solid state switching element
allows switching ON at any time during the AC cycle, relying on the
Load Current zero crossing to turn off the Triac. Because of this,
the UCD relies on the Load current waveform for
synchronization.
[0184] Inductive loads cause the current waveform to shift in real
time as dimming levels are adjusted. Advanced line synchronization
and triggering techniques implemented in software minimizes this
phase shift for stable dimming, however not completely. Without
center switching, the average current waveform delays further and
further relative to the applied voltage waveform as dimming levels
are increased, resulting in a low power factor which wastes
available power. Linear current control is possible with a Triac.
At high dimming levels, load current doesn't even begin to flow
until substantially after the peak applied voltage is reached,
significantly reducing the magnitude and remaining available time
for current to flow through the load. Since current does not flow
during the peak applied AC voltage, this limits the maximum firing
voltage available on the secondary of a magnetic ballast and
significantly limits maximum realizeable dimming levels.
[0185] FIG. 12C shows the Applied AC voltage waveform 1198, the
load current through the Triac 1255, and the phase-shifted
(delayed) current waveform 1265 that results in a power factor that
is not as good as achieved by way of the LCD 1100 of the first
embodiment.
[0186] FIG. 13 shows a schematic diagram of a preferred
construction for implementing the LCD 1100. For convenience, a
Microchip PIC processor 1310 provides the timing and logic
functions for the LCD 1100. Other devices, configurations, or
technologies could be considered for providing such functions for
the LCD 1100 while remaining within the scope of this invention. An
Operational Amplifier U3 is used to drive the gate of the MOSFET Q1
(whereby the MOSFET Q1 corresponds to the MOSFET 1120 shown in FIG.
11). In the Linear mode, the OP amp U3 senses the load current via
the voltage developed across the current sense resistor R12 and
linearly controls the gate voltage of the MOSFET Q1 to maintain the
specified current indicated by the Digital to Analog converter
output of the Processor PIC. When in the Center Switching mode, the
Processor PIC offsets the OP amp U3 via a tri-stateable digital
output to turn the MOSFET Q1 completely ON or OFF. The high slew
rate of the OP amp U3 facilitates fast Gate control of the MOSFET
Q1. Preferably, a rail to rail OP Amp device is selected to
eliminate the requirement for a negative supply voltage.
[0187] The bridge rectifier D8 is in series with the Load, whereby
it converts the bi-directional AC load current into a
uni-directional current flow, compatible with a single MOSFET
switching element, which greatly simplifies the gate biasing
network. The 8 bit PWM output of the Processor PIC is used as a
Digital to Analog (D/A) output for linear current control of the
MOSFET Q1. A simple 2-pole RC low pass filter (resistor R6 and
capacitor C6) converts the PWM output to a microprocessor-commanded
stable DC voltage level. A voltage divider (resistor R13 and
resistor R9) matches the D/A output to the sensed current. The +12V
and +5V supply voltages are derived from voltage across the Bridge
rectifier D8 (corresponding to bridge rectifier 1110 in FIG. 11)
during times when the MOSFET Q1 is turned OFF. A large capacitor
(C2, C5) is charged and Zener regulator diodes D1, D3 provide
stable supply voltages.
[0188] In the preferred construction of the first embodiment, only
7 milliamps of 5V supply and 3 milliamps of +12V supply are
required for powering the LCD 1100. In the preferred construction,
the processor PIC is a PIC16C772 device made by Microchip. The
PIC16C772 includes an internal 4 MHz clock oscillator, one 16 Bit
timer, one 8 bit Pulse Width Modulated (PWM) Output, 5 twelve bit
Analog to Digital conversion channels, 4 Kilobytes of Flash program
storage memory, and 256 bytes of Random Access Memory. Other
processor devices can be considered for the LCD without impacting
circuit functionality, while remaining within the scope of the
invention.
[0189] The 16 bit timer is used for MOSFET control timing within
the 16.67 millisecond AC waveform period. The use of a 16 bit timer
facilitates quite accurate center switching timing control (500
nanosecond timing resolution). Accurate timing is required so that
symmetrical switching of the MOSFET can occur, resulting in
flickerless dimming. This timer is reset at each AC voltage
waveform zero crossing and free-run counts up from that point. A
high valued resistor R3 protects the synchronization input pin of
Processor PIC from excessive input voltages. Software run by the
Processor PIC calculates the proper timer count to switch ON or OFF
the MOSFET Q1 based on the commanded dim level potentiometer (for
example, see the description with respect to the different
constructions of the UCD described previously). Once the proper
timer value is reached (determined by software sampling of the
timer), software places the tri-state digital output into it's
proper state. This output is driven Low (zero volts) to force the
OP Amp output to slew to it's positive rail (to turn the MOSFET Q1
fully ON), driven High (5 Volts) to slew to it's negative rail (0
Volts to turn the MOSFET Q1 completely OFF), or go tri-state (or
high impedance) to linearly control the gate voltage of the MOSFET
Q1 for current control). Using this method, the PWM D/A output of
the Processor PIC remains static and only changes when the Dim
Level changes, resulting in very accurate timing.
[0190] Like the other described constructions of the UCD, the
two-wire nature of the LCD device, whereby the LCD device wires in
series with the load, is maintained, whereby it requires no
specific connection to the neutral or safety ground. Accordingly,
replacement of a SPST wall switch with the LCD can be easily
performed.
[0191] The software written for the Linear Dimmer is preferably
written in "C", using Microchip PIC software development tools. See
the description of earlier embodiments of the invention for
software that may be utilized for the Processor of the LCD. This
dimmer configuration works by maintaining a constant load current
in accordance with the D/A converter voltage output from the
PIC.
[0192] Since the local supply voltages for the microprocessor, OP
Amp, and MOSFET drive is derived from the MOSFET "OFF" time,
periods where the MOSFET Q1 is off (or has significant voltage
across it) are maintained so that the supply voltage does not drop
too low. Since only a few milliamps of supply voltages are
required, this required OFF time can be quite short. For brief
periods (on the order of 0.5 msec) bracketing the voltage zero
crossings, the MOSFET Q1 remains OFF. Leaving the MOSFET Q1 OFF for
this very short period of time during the Voltage zero crossing
does not affect the full intensity level of the lamp. Since the
positive voltage pulses occur at 120 Hz (60 Hz with the UCD and
UCD-2 configurations), capacitive coupling of the supply voltages
using a small value capacitor (C8 and C9 in FIG. 13) minimizes
power dissipation in the power supply circuit.
[0193] In a preferred implementation of the LCD, light output is
controlled based on the position of the operator controlled Dim
Level potentiometer, in conjunction with sensed ambient light
indicated by the Optional Photo Conductive Cell (PCC). Varying
ambient light causes the PCC to change resistance, forming a
voltage divider with R6, as seen in FIG. 13. If the PCC is not to
be used, a 1K ohm resistor may be substituted instead. The Dim
Level potentiometer voltage is read in software by the A/D
converter function of the Processor PIC, and scaled to a value
corresponding to a "reasonable" PCC voltage divider A/D conversion
reading. The software encoded for the Processor PIC incrementally
adjusts the pulse width and D/A converter output voltage so that
the ambient light (as indicated by the PCC voltage divider
conversion) matches the Dim Level voltage reading. Using this
procedure, ambient light is power efficiently controlled, using
only that lamp power required to maintain the operator desired
ambient light level.
[0194] At initial power on, the fluorescent lamp should be fully
heated at full intensity before it is dimmed. The period of time
required is approximately 15 to 30 seconds. After this initial warm
up time has transpired, the LCD incrementally adjusts the Lamp
intensity level corresponding to the Dim level potentiometer
position.
[0195] Depending on the specific installation (Number of fixtures,
and Commanded Dim levels), it is possible for the MOSFET Q1 to get
excessively hot. As a safety feature, a thermistor RT1 is thermally
coupled to the MOSFET Q1, whereby a thermistor changes its
resistance in accordance with its temperature. The thermistor RT1
is placed into a voltage divider circuit with resistor R1, causing
a varying voltage (Readable by the A/D converter of the Processor
PIC), corresponding to the temperature of the MOSFET Q1. At a
MOSFET temperature of approximately 50 degrees C., software being
run by the PIC will begin incrementally increasing Lamp intensity
so that MOSFET power dissapation and temperature is reduced.
Accordingly, a protection mode is provided for the LCD 1100.
[0196] Note also that the ground symbol shown in FIG. 13 is a local
ground return and does not imply a connection to the line neutral
or safety ground. Accordingly, the LCD 1100 truly is a two-wire
device. Also, a photoconductive cell PC1 is shown in FIG. 13, to
provide an optional feature of automatic dimmer control based on
the amount of light sensed by a light sensor S1. The
photoconductive cell PC1 senses the amount of light received by the
light sensor S1, and provide an input signal to the processor PIC,
which the processor PIC uses to set the amount of dimming to be
performed by way of the LCD 1100.
[0197] A preferred embodiment of the present invention has been
described according to the present invention. Many modifications
and variations may be made to the techniques and structures
described and illustrated herein without departing from the spirit
and scope of the invention. Accordingly, it should be understood
that the apparatuses described herein are illustrative only and are
not limiting upon the scope of the invention. With the use of an
energy savings device according to an embodiment of the invention,
it is possible to achieve up to a 60% or more energy savings, while
not adversely affecting the perceived amount of light by users.
[0198] Also, the above-described embodiment of the present
invention is capable of providing dimming for electronic ballast
fluorescent fixtures, using the same electronics and software as
those described earlier with respect to magnetic ballast
fluorescent fixtures. Tests performed by the inventors showed a
dimming capability for several different types of electronic
ballast fluorescent fixtures, without any noticeable flickering.
Therefore, an apparatus and method according to different
embodiments of the present invention can be used to control
resistive, inductive, and/or capacitive loads, and even to control
dimming of fluorescent light fixtures that are configured to screw
into incandescent light sockets.
* * * * *
References